It's no secret that virtual desktop infrastructure involves significant storage costs, but the problem is exacerbated by vendors that vastly underestimate storage requirements.

Meanwhile, new hybrid solid-state storage products for virtual desktop infrastructure (VDI) reduce the storage problem and -- finally -- bring the cost of virtual desktops to the level of PCs.

Many VDI pilots start out with a small pool of virtual desktops that any old storage system can handle, so conceptually, everything works. But as companies scale out, storage becomes the root cause of performance problems, and desktop virtualization quickly turns into a money pit.

Part of the problem is that vendors vastly underestimate the storage that will be needed. They use best-case scenarios when specifying product infrastructure requirements during the product sales process, said Rick Varju, director of engineering and operations at Foley and Lardner LLP, a Boston-based law firm.

After working with VMware Inc. through the initial stages of an early-adopter View deployment project, Varju said he learned not to underestimate VDI storage requirements. He heads the law firm's VDI deployment initiative.

"The difference between what was initially specified and what was actually required from an infastructure perspective was off by as much as 50%," Varju said. "This was true not only for storage, but also for VM host, server CPU and memory requirements."

Billion Automobile, a Midwest-based GMC auto dealership with 16 locations, had a similar exprience when it recently put 500 of its 900 employees on VMware View virtual desktops.

"[The vendors] come in and say, 'You have enough storage; you will never use all of it up,'" said Tom Likely, IT manager for the auto dealership. "But it happens soon enough."

"We did factor that into our storage planning efforts with VMware and a storage vendor using information provided by VMware at that time, and [we] ultimately ended up missing the mark," Varju said. "It was a real eye-opener, as you can imagine."

When Foley and Lardner upgrades from Windows XP and Office 2003 to Windows 7 and Office 2010 this year, resource demands will increase, and the firm may need even more hardware.

The problem is not unique to VMware customers, said Dan Bolton, systems architect for Kingston University in the U.K. He did proofs of concept on just about every desktop virtualization product out there before settling on Quest Software's vWorkspace in 2011.

"Everything VMware, Citrix, Quest and others claimed about storage reductions and beating the IOPs battle, I took with a pinch of salt," Bolton said.

Bolton chose Quest because its technology met his organization's needs at the right price.

VDI storage problems: Who's to blame?

VMware, for its part, puts the onus on customers to determine their own VDI storage requirements and insists that proper planning can stave off the need for massive infrastructure upgrades.

"The up-front assessment, done either by a partner or by the customer, is where you get an understanding of the application needs, what users are doing on the network [and] the current infrastructure," said Mason Uyeda, a spokesman for VMware's end-user computing group.

"We see issues where the assessment wasn't comprehensive enough, where an administrator didn't realize that their end users needed as much as they did." Those customers have to throw more hardware at the problem, Uyeda said.

While reference architectures and storage best practices can help, IT administrators who are new to VDI can't possibly know how to architect a complicated virtual infrastructure -- which involves networking, storage, servers and desktops -- without performing test benchmarks against real workloads, Bolton said.

"[Vendors] have technology to 'help' and white papers about what they can achieve in a closed lab, but nothing compares to real-world implementations," Bolton said. "Don't assume 20 IOPs [I/O per second] per desktop will be enough because it rarely is -- unless the end user has fallen asleep."

Administrators also need to understand that traditional storage arrays that work fine for virtual servers aren't designed for virtual desktops, experts said.

That's what Ryan Goessling, infrastructure architect for the California State Teachers Retirement System (CALSTRS), learned when his team deployed VDI in the same way they did their server virtual machines.

"We were using three SAN [storage area network] devices for virtual servers and tried to mix server and virtual desktops on them," Goessling said. "It didn't work out. … We ran into bottlenecks with storage, CPU and RAM."

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Just to be clear, missing the mark on our initial storage calculations did not jeopardize the ultimate success of our VDI deployment at Foley & Lardner LLP. We certainly had to make the necessary adjustments to right size our storage and server cluster hardware as moved farther into our deployment, but it has been a good move for us and VMware has been with us every step of the way. We now have over 1700 desktops virtualized and our move to VDI has positioned our firm to securely embrace BYOD in a big way, which has been another huge benefit for us. Despite some of the early adopter pains we experienced early on in our VDI deployment, we’ve now been enjoying all of the gains and benefits that come along with VDI. In fact, the combination of VDI and BYOD are now saving our firm upwards of a half million dollars annually. That’s a huge success in my book.